Variable terminal impedance signaling system



June 29, 1937. M. G. CROSBY VARIABLE TERMINAL IMPEDANCE SIGNALING SYSTEM Filed Dec. 27, 1933 /fgw 4 Sheets-Sheet l INVENTR MURRAY @CROSBY ATTORN EY .June 29, 1937'.

M. G. CROSBY 2,085,418

VARIABLE TERMINAL IMPEDANCE SIGNALING SYSTEM CARR/El? WAVE JOl/HCE /2 (ARR/ER WAVE SOI/RCE Filed Deo. 27, 1935 4 Sheets-Sheet 2 INVENTOR MURRAY @CROSBY l BY ATTORN EY I June 29, 193m M. G. CROSBY VARIABLE TERMINAL IMPEDANCE SIGNALING SYSTEM Filed Deo. 27, 1955 4 Sheets-Sheet 3 INVENTOR MURRAY 6 CROSBY vkw ATTORNEY `une 29, 1937. M. G. CROSBY 1 VARIABLE TERMINAL IMPEDANCE SIGNALING SYSTEM Filed Dec. 27. 1935 larg,

4 Sheets-Sheet 4 Eggs TUBE /0 INVENTOR MURRAY Gv CROSBY E Wigm ATTORN EY Patentedy June 2 9, 1937.

fzossalt z VARIABLE TERMINAL mPEDANon sm- Namo. srs'rnu- Murray G. Crosby, Riverhead., N. .-Y., assignor to Radio Corporation of America, a corporation of, Delaware v Application December anlass, seriamo. '104. 12i 2s claims. (c1. iis- 171) 'Ihis invention concerns a new methodoi and means for producing impedance variations, ap-

plying the same to the terminal of an articial line or filter' circuit on which carrier waves have 5 been-impressed to produce' relative changes in the reected and incident wave, and of utilizing said changesior signaling. 1

More speciiically, 'this inventionrelatesto a new method of and means for a phase and amplii tude modulation wherein the terminating imped- 'ance of aretardation' circuit, such as an artiiicial line or wave lfilter, is in accodancelwith the present invention modulated to produce a phase or amplitude modulationiof the .voltage at certain `15 points on the line. By varying the terminating impedance 'of such a circuit, the amplitude 'of the reiiected wave iscaused to vary-so that the resultant voltage at certain points on the line, due

to the combination, of the lincident and reflected waves, is variedv in phase, and the resultant voltage at other points on the line is varied in amplitude. Consequently, by choosing the voltage at the proper point on the retardation circuit,

either phase or amplitude modulation vmay be ob tained.

In the prior art 'oiphase modulation, the variation in phase has usually been accomplished by dierentially amplitude modulating two like frequency carriers adjusted to be less than 180 de'- queritly,` a new approach'is 4proviffed to the problem o1'.v producingamplitude modulation of acar.- rier wave which is linear in accordance with the f Signal.

In one modificationI oi my invention a simple push-pullarrangeme'nt 'of-lines' 'or retardation 'circuits and tubes isprovidedtoenhancethe ease of obtaining linear phase 'or'amplitude mod ulation. In another modiiication the advantases of the push-pull arrangement ,may be obtainedin va single line' or circuit and. as'ingle'ftube An apparent advavantage,V o! the V,controlling dea vices or modulatorswhereinqdescribedfia that by the use of one Vcircuit.many'jdii'iferenttypes oi modulation are, made available. i-n the push-pull modification., amplitude modulation, carrier eliminated amplitude` modulation,l andphase modulation are obtainable with approl priatealternative` adjustments for each.

The novel features oi' my invention pointed out with particularity in the claims apl pended hereto. l

The nature of my invention, the methods of signaling involved, and the Vmeans. where y said methods are carried outwill be better'understood 25 -from` the following detailed description thereof andtherefrom when read in connection with the drawings, throughout whichllike rference char-- acters indicate like parts. and in which:

For instance,

haveV been grees apart in phase and combining these two'l Figure 1 shows the essential elements of one 30 modulations. See United states application No. Aof my novel circuits by incenso! which the char- 588,309, led January 23, 1932. The modulator acter of vvarying potentials may be controlled in, of the present'disclosure broadly relates to the a novel way in accordance With my present 1nprinciple concerned in the said Crosby' applicavention;

351tion except that here the 4controlling variations Figures 2te' Sinclusive'and 10V show variouscir- 35 are utilized in a novel manner to 'control the tercuit arrangements in which the method of vand minating impedance of a line along-which the means for controlling the character oi varying carrier frequency travels andthe inherent 'propt Currents. 8S DOintedOut'ln connection'with F13- erties of v said artiiicial line or wave iilter so con' ure 1, have been utilized fOr'VTyinSat Signal fl'A 40 trolled are utilized to produceboth the phase quencyacarrier waveywhile,

or amplitude control which illustrates the funda- 45' variation' in amplitude is usually produced by mental principle involved in the wave controlling varying an element voltage o; a thermionic amor modulating devices vof the present inventionl:y

- plifier. In the present vinvention a variation of The voltage to be varied in phase or amplitude ls voltage between elements of a y)thermionic tube applied at I, thence to tunedcircuit 2 and vto the causes an impedance between the same or, other couplingtube 3. The voltage applied to l may be 5o tube elements to vary. This variable impedance of any frequency and amplitude., Voltage is fed so produced is utilized as the terminating im- ,to the anode ofv tube 3 from" source 5 by way of 'pedance of a retardation circuit or line or artiradio frequency choke 4. The alternating voltoi'al line so as to amplitude modulate the reage is amplified in 3 and is fed to line 6, which is iiected wave of voltage in the circuit. Consechanges and the amplitude changes desired in the travelling wave. vHence, by this novel combinatiorl of operations, adjustments are made fewer and complications'reduced. .4

In the prior art of amplitude modulation, the

Figure 1 shows a diagram of a phase shifter terminated by a variable impedance 8. The ,kn- 55 Y 40 ctor diagrams illuspedance 8 may be resistive, as shown, or inductive or capacitive. An output coup1ing tube I0 ref ,ceives its control grid energy from ythe line G bywayr of tap I2 through blocking condenser 7.

Grid leak resistance 9 furnishes operating bias` tothe control grid vof tube I0. 'I'he energy pro. duced by the arrangement is taken fromitransformer II and maybe utilized i-n anymanner.

^ Figure 2 illustrates a sig'nalin :circuit including among. other features a phase plitude modulator utilizing the principle involved in the circuit of Figure 1 except that the variable impedance 8 of Figure 1 is replaced by the anode to cathode vimpedance of a modulator tube 8. This modulator tube receives its anode voltage from battery, 5 by way of radio frequency choke 4 and the induc'tanceof line 6. The controlling wave which'may bea signal is impressed onv the tures as shown connected 'as shown including switches 2I, 22 and 23,. the

purpose of which will vbeset forth in detail hereinafter.

Figure 4 shows'the application of anode modulation which may be appliedto either of the circuits of Figures 2 and 3 as an alternative method of varying the plate impedance of the'tube1 8. The modulation is applied on jack I3, Via transformer I4 and radio frequency choke RFC, to

' lthe anode of the tube 3. Condensers I8 and'20 are blocking and by-pass condensers respectively.

G'is the line or lter circuit of Figure 2. In the push-pull arrangements -two modulator tubes, 3

and 8', connected as shown in Figure 5, may be used. In this case the control tubes are fedlby l a push-pull modulation transformer It as shown inFigure 5. Y

Figure 6 shows a screen grid tube utilized as a modulator tube im accordance withLthe present invention. The circuitl of Figure 6 is otherwise similar to the circuit of Figure 4. The controlling l voltage is fed through jack I 3 and transformer M to the screen grid electrode ofthe modulator tube 8. The varying potentials applied to the screen grid 'of this tube vary the characteristics thereof such as'the amplification factor, theinternal impedance conductivity, etc. .The variations between the ianode and cathode of 8 are applied to the `terminal of I ine for the purpose specied.

In Figure 7 vector diagrams are given to aid in lthe explanationof operation of the invention. 'I'he operation ofthis phase varier amplitude modulator 'carrier velimination modulator depends d .upon the fact that when a retardation circuit,

consisting of an articlal line or wavefllter, is not terminated by an impedance equal to the characteristic impedance o f fthe 'retardation circuit, 'a reection occurs at the termination ofthe line and standing waves are formed along Athe line. 'I'hese standing waves consist of alternate points and reected waves. HenceQwhenvthe reflected wave is in phase with the incident wave, a maximum will occur, due to the addingvof the twoA 'waves.` Likewise, when the reflected wave is in y opposite phase with respect tothe incident Wave, a minimum will occur. The phase of combination of the two V'waves depends upon the point of odulator or am- -as lshown in diagram c of Figure 7. .amplitude of the voltage at the point of tap-oi` Taoeaiie the line selected. Betwejen the points of maxima and minima the phase of combination is an angle which varies between zero and 180. degrees. Thus, for points between maximaA and minima, as theamplitude ofthe reiieted wave is varied, the resultant of the'combination is varied in phase as well as amplitude. Hence, by' choosing a point where a maximum or minimum occurs, a.

change of the terminal impedance will cause amin the energy at the tap I2 may be produced.' By Acontinuing the variation of smbetween the characteristic impedance and open circuit impedance, an additional 45 degree phase shift may be produced making a degree` total.

In Figure 7 the vector diagram a represents the condition of zero terminating impedance where I represents the current of the incident Wave, 'R represents the c'urrent of the reiected Wave, and T represents the resultant of both, currents.

en the terminating resistance 8 is varied so that R is reduced, as given by R' int vector dia' gram b of Figure 7, the resultant T is shifted or moved in phase by the amount 4. When Figure '1 is to be used as a volume or amplitude control, the top I2 may be adjusted to a. point of maximum or minimum potential with the line s open or snorted at-tne termination.

Thenwith 8 adjusted to a value equal to the characteristic wave impedance of the line, there willl be no re'ected Wave on the line. 'I'his has been portrayed by the vector diagram c of Figure 7. When is adjusted in one direction away from the characteristic .line impedance, the reflected .wave tends to buck the incident wave to iieotedwave tends to add, with the incident wave',-I

Thu's, the

l2' varies, dependent pedance 8.

upon the value of the im-- 'i Figure 2 shows a signaling device including a modulator circuit making use of the same principles as' the'phase and volume control of Figure 1 except that the terminating impedance 8 of Figure 1 is replaced by the anode to 'cathodev impedance of a modulator tube 8 so that the terminating impedance mayebe varied at the 4fre' quency rate of the signal weve applied from the controlling potential source by way of jack I3 to the control'grid ofO. Thus, by adjusting tap i I2 to a point of maximum, as described in connection with Figure 1, amplitude modulation of the carrierawave from source I is effected. Likeawise, by adjusting the tap I2 between maximum ont current or voltage maxima or minima d ue to the resultant of the combinationv of the incident vand minima, phase modulation of the Wave from I is effected in the manner described in connection with Figure 1 when used as a phase shifter.

'I'he push-pull circuit of Figures 3 and 5 lend themselves to many arrangements Afor producing amplitude and/or carrier elimination and phase modulation.

In Figureis8 of the drawings the curve shows the voltage distribution 'of asection of the v 2,085,418 fline 6 ort"andbelowfitare.shown'the vector diagrams of the incident and reiiected voltages.

I and-R. for the lf voltagefpoints on the lline indicated by the dotted lineswhich extend from the'vectors to the curve' a. The table of Fig- `ure v9 "showsfeight of the possible` combinations which may beh'a/d'with this circuit. Aside from l the various line adjustments, as portrayed by the other words, in paralleler differentially to thel vveztordiagrams of FiguresS and `9, there Vis the possibility of combiningthe radiofrequency enlergy in .parallel or differentially. With the parallel radio frequency combination switches- 22 and 23 are both moved into the right hand closed position for cophasal addition of theunmodulated carrier inthe windings 2 and 2 and of the controlled wave in transformer I I. With the difmodulator tubes.

-The table of VFigure 9 illustrates the different types of modulated output obtained under certain circumstances anddlfferent positions of the taps I2 and I2' on the lines 6 and 6'..

' For instance, in the. iirst column the first line indicates thatone artificial line tap, (say I2) .would be on vpoir'it-flf'of Figure 8 and the other line tap (say I 2) would be on point 3 of curve 8 of Figure 8. Tlie"second column l(first line) indicates the vector relations of the incident and reflected currentslonjthe two lines at theA tap points selected.' The third column (first line) indicates the radio frequency combination of the 'carrier as determnaifby the position of switch 22 `and the modulated-.carrier combination as determined by switch 23.v Right hand closed for cophasal addition in parallel combination and 'either one moved Ato left hand closed for difierential combination .*1he fourth and fth columns give the resulting. output, modulated or otherwise for the two manners of applying the carrier to the line.

In the samervmanner, the other cases of the table of Figure 9 showr the adjustments for the other types 'of'modulatiod' These main cases .show the principal variations. vOther adjustments may also' be made which are between the adjustments shown.

In thevar'rangements where a phase shift or modulatlonls accomplished, there might be an amplitude change introduced` as Well as a phase change. This amplitude change may be removed by passing the shifted orA modulated energy through amplitude limiters whose output remains constant regardless. of the variation of the input withlnfcertain'limits', .A thermionic tube which is loaded to saturation will serve as an amplitude limiter.`

It willbe apparentthat my invention contemvplates the useof screen grid or multi-element tubes in' place of the triodes shown in the prior figures.' Triodes are employed merely for 'dlagram simplicity.

Figures 4 and 6'show how plate modulation and screen grid Vmodulation may be employed to ulation is'employedin Figures 2 and 3.

modulate thefplate impedance of the modulator tube in the same manner that control grid mod- In Figure 4 the tube 8 is connected as shown Vto apply the modulating potentials from any source byway ofthe jack I3 and transformer I4v to the anode electrode. .The anode circuit includes, as shown, the secondary winding of the transformer Il in parallel with a capacity 20, both of which are in series with radio frequency choking inductance RFC. The modulating potentials are applied by way of a coupling condenser I8 to the terminal of the line .6 fso that here, as in the. prior case, the terminal lm- -pedance of the line 6 comprises the anodeto lcathode impedance of the modulator tube 8. The

capacity I8 is small enough to preventthe controlling frequency energy from reaching the line 6, but is large enough to insure connection ofthe impedance between the anode and cathode of 8 to the terminal of the line 6.

In Figure 6 the tube 8 is ofl the screen grid type.` Here the anode to cathode impedance is connected in parallel with the terminal of the lin'e 6 and the modulating potentials are applied it is accomplished in Figure 4. Figure 5,

however, includes the switches 2|, 22 and 23 shown in Figure 3 and described in connection with Figure 3. -The switch 22 permits carrier waves to be applied in opposition or in phase to the artificial line 6. The switch 2| permits the controlling voltages to be applied in parallel or in opposition to the modulating tubes, while the switch 23 permits the controlled wave to b/e added in phase or in phase opposition before application to the utilization circuit.

yIn -Figure 10 I have shown a simplified single coupling tube and single artificial line which permits attainment of the results obtained with' the push-pull type circuits ofY Figures 3 and 5. The carrier from I may be applied as shown by way of thecoupling tube 3 to the line 6 and from theline 6 by way of tap b and switch S to the control grid and by the tap I2 to the control grid of I0'. Here as in the prior arrangements` the terminating impedance of line 6 is varied at signal frequency so that the reflected wave on the line s shifts relative to the incident wave to produce aresultant that shifts as to amplitude or as to phase or both.

With the switch S connected to b as indi.

cated above. the wave form along the line 6 being as indicated at a in Figure v8, the taps b and I2' may be moved to various points 'on the line E to produce all of the various outputs shown in the fourth column of Figure 9 resulting from the simpliedcircuit of FigureVlO when operated above gives the sameoresults as the arrangements of Figures 3 and 5 when switches 22 and 4 23 are in the right hand closed position.

With switch S of Figure 10 on wire a, the

vector relations of the voltages on tubes 4Ill and -Ill' with the line tap on point I of Figure 8v are shown in Figure 11 a.

co parallel modulation of the tubes. In other words Any other system of modulatingy an impedance may be employedwhether the system includes thermionlc tubes or not. Mo'reover in some cases the lineA may require some reactance in addition to the. ohmicl resistance shown.at its terminal to damp it. I contemplate addingrthe necessary reactanceeither inductive r capacitive in parallel'or in Iseries with the tube impedance or with -thev resistance at the end of the line of l 'signalingpurposes 1.2111@ method of signaling by containing the phase relation of reflected and. incident waves on a transmission line to which said. incident waves have been applied, said transmission line being terminated by a variable impedance which includes thesteps of varying said variable impedance terminating Vsaid line at signal fre` quency and derivingv energy from said line for 2. The methodof signaling by Varying dent waves along a line the terminal of which tube 'and to which line the incident waves have" been applied which includes the -step of varying the impedance of said tube at'signal frequencyl. 3. The method of signaling by varying 'the combinedA characteristicof reflected. and moident ywaves along a line terminated' by an 'impedan'ce to which line the'incident waves have been-applied which includes the steps of, vary- -ing the said terminal impedance o f said line ai `signal frequency and utilizing resultantenergy from said line for signaling purposes. Y

` 4.'The method Loi producing-variations in the characteristic of carrierwaves at signal frequency whichl includes the steps. of, impressing said waves on a transmission .medium having a predetermined terminal impedance inA which lmedium standing and incident waves are produced, andvarying the yterminal impedance of said mediumat signal frequency.

5. The method of producing variations inthe characteristic of carrier waves at signal frequency which includes the steps of, generating' carrier waves, impressing said waves on a transmission medium terminated by an impedance,

'producing signal potentials, and varying kthe terminal impedance offsaid medium at the frequency of said signal potentials. .I

6. The method of producing carrier. waves,

one or more characteristics of which vary in accordance with modulating potentials which includes thesteps of, impressing a carrier wave on a transmission .mediumofl known terminal impedanceto produce in said mediumY an incident and a reected wave, varying the terminal impedance of said medium in'accordance with Vthemodulating potentials to produce relative changes in the reflected "and incident wave, and

5 diverting energy from said mediumat a selected 70V point to produce the desired variations characteristie-of the modulating 'potentials in the'energy resulting from the diverted combined incident and reilected Wave. 'i t 7. The method of producing carrier waves, one or more 4character isticsof whichvary in acthe 'combined characteristic of reiiected .and inci- 30 vsordi-nwe"with modulating potentials fwmch int 1 cludes the stepsof, impressing a carrier wave on a transmission medium 'of variable shunt impedance to produce inv said medium an incident and a reected Wave, simultaneously varying the shuntingimpedance of said medium in cordance with the modulating potentials to produce relative changes in the reflected and incident wave, diverting energy from said medium at a selected point to produce the desired variations characteristic of the modulating potentials in the energy resulting from thediverted combined.

incident and reflected `wave and transmitting said energy. y

8. The method of producing carrier energy,

the phase of which variesat signal frequency which includes thesteps of, applying said' car- )rier energy to a transmission medium of prede-` 9. A-circuit mvpontromngithe characteristics i ao of a carrier wave including. anartificial line `having series inductance and parallel capacity and terminating -in an impedance. the value of which is such as to normally eliminate standing waves along said line, means for applying said carrier wave to. said line, and means'for varying l the impedance at the terminal of said line at signal frequency to produce incident and refiected waves along said line of varying phase and amplitude, to--thereby lproduce a resultant of the'incident 'andreected wave alongthe line of amplitude andlphase which varies in accoi-dance with said signals. o g

10.- A circuit for controlling the characteristic of a carrier wave including". a pair of artificial lines-each having series inductance and parallel capacity-and terminating inan impedance, the value of which is suchV as tonormally eliminate standing waves along said lines, means for applying said carrier wave to said lines, and means for-varying the impedances at the terminal of said lines at signal frequency to produce inci- 1 dent and reected waves along sagd line of a phasewhich varies Aat signal frequency. `11. A circuit for controlling theicharacteristics of a carrier wave including, a pair of-articiai 20" ilected and inlines each having series inductance and parallel capacity and terminating in an impedance which includes theimpedance betweenv electrodes in a thermionic tube, means .forl applyingsaid carrier wave. to theinput terminals of said lines to produce incident and reflected waves therealong,

, means for varying the impedance of said tubes at signal frequency to thereby vary the phase and amplitude of the resultant o f the incident and reflected Wave along the lines in accordance with said signals, and a movable tap-on each of said' lines for diverting therefrom energy which is a resultant of incident and reflected waves of thev desired phase relationship.v i

12. .Means for modulating the phase of 'a carrier i Wave at signal frequency comprising an artificial transmission line including series Yinductance and parallel capacity, said line being terminated by an impedance, means for applying the carrier wave to be varied to the input terminal of said line aos-5,418

the combined reflected and incident wave in saidline, means for selecting energy from said line at a point between one of said maximum and mini'- mum points, and means for utilizing said selected energy for signaling;

13. A device for modulating the amplitude of carrier frequency waves at signal frequency comprising anartiiicialfline including series inductance and parallel capacity,

waves to be modulated to the input terminal of said lineto produce incident and reflected waves' thereon, means for varying -the terminal impedance of said line at signal frequency to produce points of maximum and minimum in the resultant of the combined incident and reflected wave, and

means for selecting energyfrom a point onl said line at which a minimum or maximum occursl Y and utilizing said energy for signaling.

14. Meansfor modulating the phase of a carrier wave at signal frequency comprising an articial transmission lineincluding series inductanceA and 'parallel capacity, said line being terminated by the impedance between the electrodes4 in a thermionic tube, means for applying the carrier wave to be varied to the input terminal of said line whereby reected and incidentwaves of variable phase relationship' are set upin said line, varying said Atube impedance to produce points of maximum and minimum in the combined reected and incident wave in said line, means for selecting energy from said line at point's between maximum and minimum energy points on said line,and a pair ofthermionic tubes having-their control grids connected to said last named means.

15. Means for modulating the pli/'ase of a carrier wave at signal frequency comprising a pair of articial transmission lines each including series inductance and parallel capacity, said lines. each being terminated by the impedance between .eleci istic of a carrier wave, a pair of lines each having v reactances, and 'each being connected with an trodes of a thermionic tube, means for applying the carrier wave to be varied to the input terminal of said line whereby reflected and incident wavesof -variable phase relationship are set up in said line, means for varying the impedances of-saidtubesin paralleler in phase opposition'at' signal frequency to produce points of maximum and minimum in the combined reflected and incident wave in said line, which shift at signal frequencies, a pair of thermionic tubes'and a connection between a point on each line and an electrode in each of said tubes.

v16. A device fo'r carrier waves at signal frequency comprising a v'pair vof articial lines each including series inoi' said lines to produce incident and 'waves thereon, a circuit for applying modulating ductance and parallel capacity, said lines each terminating bythe impedance between electrodes in a. thermionic tube, means for applying the carrier waves to be modulated tc the input terminals reflected potentials lin the desired phase relation to like electrodes in each of said ltubes to produce shift' ing points of maximum .and minimum inthe resultant of the combined incident and reected wave, tubes each having a control'electrode connected to a selected point on a dierent one of said lines and output electrodes coupled to said work circuit.

, 1'1. Means for varying he phase and amplitude i l lcoupling the input of said line to said source of 75 of carrier waves at signal said line terminatingv in an impedance, means for applying the carrier` modulating the amplitude4 of a work circuit and a pair of thermionic frequency comprising..Y A

an artificial line having itsinput'terminals energized by the carrier wave and its output terminals connectedv with a variable impedance, and therldiverting energy from said medium at selected points, combining said energy differentially or additively and signaling with the resultant of the combined. energy. Q I

19. In a phaseinodulatoiyeJ source of carrier wave oscil1ations,a source of signal potentials,

a thermionic tube having a plurality of electrodes,

a transmission line comprising series and parallel reactances, a connection between one end of said line and said nectlng a pair of the electrodes' ofsald tube in shunt to said line, anda 'connection between said source of signal potentialsand a pair of electrodes in said tube'. n, v

20. In a circuit for controlling the characteristic of a carrier wave, a reactive line terminating in an impedance, the :value of said impedance being. such4 'as to normally' eliminate standing waves along' said ,line whenv energized by said carrier wave-means for applying said carrier wave to said line and means for varying the imf pedance at the terminal. of said line at 4signal frequency, to produce incident and reected waves along said line of varying character to thereby the incident and reilected produce a resultant of wave along the line, tlie character which varies in accordance `with said signals.

2l. In a circuit forcontrolling the characterimpedance which may be varied, means for applying carrierfwave energy to said lines to produce in said linesy incident andlreiiected waves, means for varying said impedances at signal frequency to thereby vary the phase and amplitude of the inductive and capacitive reactances,l said line terminating in an impedance, means for applying the oscillations to be, modulated to said line toV produce in said lfne incident and reected waves,

means for varying the terminal impedance of source of oscillationaa circuit consaid -line-at signal frequency to producepoints of maximum and minimum for selecting energy from points on said lines at in the resultant of the combined incident and reflected waves and means combined waves and utilizing said selected energy i for signaling.

" 23. In a' signaling system, 'a source-of oscillations 'of carrier wave frequency."a load circuit, a source of modu1ating line comprising serlesand parallel reactance's, said transmission line lhaving an input, a circuit potentials, a transmission' 

